A performance of a wet plate clutch may be affected by the operating conditions the clutch is operated in. In addition, certain operational parameters of the wet plate clutch may also be affected by the current and past operating conditions. Such uncertainty of performance or operational parameters may be a result of production tolerances of the wet plate clutch, temperature effects on the wet plate clutch, and wear of the components of the wet plate clutch. By adjusting a set of filling parameters used with the wet plate clutch through a learning process over time, such problems can be overcome.
When a stepped ratio transmission is shifted, clutches of the transmission are engaged and disengaged to facilitate a power transfer through a selected power path and a selected gearing. Typically, when a shift is performed, a first clutch is released (also known as an off-going clutch) by decreasing an oil pressure on a first clutch piston. Simultaneously or shortly thereafter, a second clutch is closed (also known as an on-coming clutch) by increasing an oil pressure on a second clutch piston. Such a shift may be commonly referred to as an “overlap shift” or a “powershift.” During an overlap shift, the above described process happens simultaneously in a coordinated manner. In a filling phase of a shift, the second clutch piston is positioned adjacent a set of friction plates of the second clutch by regulating the oil pressure on the second clutch piston.
The positioning of the second clutch piston is performed by sending out a pulse width modulated (also known as PWM) signal with a controller to an electro-proportional valve. In response to the pulse width modulated signal, the electro-proportional valve is at least partially opened, allowing a piston chamber of the second clutch to become pressurized. Depending on a force created by the pressure applied to the piston chamber, a position of the second clutch piston can be controlled. Typically, a goal is to move the second clutch piston as fast as possible towards the set of friction plates of the second clutch, while still being able to smoothly engage the second clutch.
An engagement profile (for applying the pressure) associated with a clutch, which is used to apply a desired movement of the clutch piston, is partially dependent on a plurality of mechanical characteristics of the clutch itself, but also other parameters such as a temperature of an automatic transmission fluid used in the clutch and an amount of air in a plurality of conduits used with the clutch. Generally, such variables are taken into account by scheduling the two parameters with which the engagement profile is parameterized.
However, calculating a correct value for each of these parameters has proven to be difficult. The correct value should be specific for a given transmission or a given clutch. Currently, values used for each of these parameters are calculated using a calibration process. The calibration process is typically performed shortly after manufacturing of the vehicle is complete and at predetermined intervals based on a number of operating hours of the vehicle.
The calibration process is performed in a single, fixed operating condition and may be summarized as a plurality of individual steps. Upon a predetermined number of operating hours of the vehicle, a transmission controller indicates that the recalibration process is advised. Once the recalibration process begins, the transmission controller operates the electro-proportional valve with a plurality of engagement profiles, each having a different set of fill parameters. The transmission controller continues this process until it is detected that the clutch has been filled in a satisfactory manner. The controller determines if the clutch has been filled in the satisfactory manner by monitoring a timing of a drop in a torque converter speed ratio. The drop in the torque converter speed ratio indicates a torque transfer has occurred through the clutch, which is indicative of a piston of the clutch contacting the set of friction plates of the clutch. The calibration process is then repeated for each of the remaining clutches of the transmission.
Using measurements from a signal from at least one sensor used with the clutch, a filling quality of the clutch can also be assessed during normal usage of the system, as opposed to during a specific calibration procedure. As non-limiting examples, a signal from a pressure sensor or a signal from a speed sensor may be used to assess the filling quality of the clutch. At least one feature is defined in the signal which is indicative of an error in the filling process. It is understood that a plurality of features may be defined in the signal or that a combination of features present in the signal may be indicative of an error in the filing process. Once the filling quality of the clutch has been assessed, a correction of at least one of a plurality of erroneous parameters can be calculated. The system and method for updating the set of fill parameters for the wet plate clutch described herein begins with a vehicle including a system capable of online learning.
A process of filling of a clutch is commonly characterized by two main parameters, a fill time and a kiss pressure. These parameters are shown on an exemplary pressure profile, which is illustrated in FIG. 1. A reference of “T_fill” in FIG. 1 indicates the fill time of the exemplary pressure profile, and a reference of “P_kiss” indicates the kiss pressure of the exemplary pressure profile. It should be noted that an apparatus and a method described herein is also applicable when more parameters than a fill time and a kiss pressure are analyzed.
The fill time indicates a length in time of a pressure profile required to fill a piston chamber with hydraulic oil and to position a piston against a set of friction plates of the clutch. The kiss pressure is a pressure following the fill time for a pressure profile. The kiss pressure indicates a hydraulic force necessary to counteract a spring force once the piston is placed against the set of friction plates. While the kiss pressure changes slowly over time as a plurality of mechanical characteristics of a clutch system including the clutch change, the fill time is dependent on other factors. Primarily, the fill time is function of a temperature and a quality of a transmission oil used with the clutch, a pressure signal used with the clutch system, and an amount of time between shifts.
Consequently, a correction on the filling parameters determined by online learning is only applicable to a condition in which a shift used for learning was performed. Further, in the implementation of the above described process, the controller saves the parameters in a multidimensional matrix as a function of a plurality of variables. As non-limiting examples, the variables may be the temperature of the automatic transmission fluid and the time between shifts of the transmission. Further, it is understood that for a given evaluated shift, the given evaluated shift likely did not occur under the exact conditions described on the grid points of the multidimensional matrix. In learning the parameters, the controller also decides how much is learned for the given points forming the grid of the multidimensional matrix.
The system and method for updating the set of fill parameters for the wet plate clutch which uses cross learning described herein solves the problems described hereinabove by proposing a structured way to update points of the multidimensional matrix in conditions that deviate from the conditions in which a given parameter was learned.
It would be advantageous to develop a device and method for updating a set of filling parameters for a wet plate clutch that improves and accelerates a learning process by using learned information to update the filling parameters for the wet plate clutch.